Similar boundary marks are already known and consist of a movable body which can move inside a corresponding housing or a casing whose upper side is open, from a working position wherein said body fixedly extends above the level of the open end of the housing, to a resting position wherein said body extends so that its top is approximately level with the housing open end.
It has already been disclosed in patent n.degree. 86 05310 filed by the present applicant that such boundary marks can be equipped with driving means, whether or not remote, consisting of a single acting pneumatic jack, for example, whose cylinder is connected to a pressure fluid source through a feeding pipe.
Other boundary marks are also known which are more simple and work thanks to manually driven mechanical means.
In all the aforesaid arrangements, the retractable boundary marks are designed to allow or prohibit access to a roadway or a place on public or private roads, for example.
The above-mentioned arrangements and therefore all the retractable boundary marks have the same disadvantage, namely they are dangerous because of the relief they form above the ground thereby creating an obstacle which is not always visible to someone inattentive due to its small height.
Of course, such disadvantage increases at night in places with poor or no lighting, or even during the day when the weather is bad.
Another disadvantage thereof appeared with the boundary marks which are driven by pneumatic, electric or hydraulic means equipped with remote control.
Actually, in the latter case, the boundary mark unexpectedly coming out from its housing in order to reach its working position can be dangerous for someone inattentive and thus taken aback.
At first, it seemed therefore necessary to focus the invention on the need to indicate the presence of such boundary marks both when they are coming out and when they are in their working position.